How do cells count?( In the 13th January print edition of...)

In the 13th January print edition of the journal Current Biology, Instituto Gubenkian de Ciencia researchers provide insight into an old mystery in cell biology, and offer up new clues to understanding cancer. Ins Cunha Ferreira and Mnica Bettencourt Dias, working with researchers at the universities of Cambridge, UK, and Siena, Italy, unravelled the mystery of how cells count the number of centrosomes, the structure that regulates the cell's skeleton, controls the multiplication of cells, and is often transformed in cancer.

This research addresses an ancient question: how does a cell know how many centrosomes it has? It is equally an important question, since both an excess or absence of centrosomes are associated with disease, from infertility to cancer.

Each cell has, at most, two centrosomes. Whenever a cell divides, each centrosome gives rise to a single daughter centrosome, inherited by one of the daughter cells. Thus, there is strict control on progeny! By using the fruit fly, the IGC researchers identified the molecule that is responsible for this 'birth control policy' of the cell a molecule called Slimb. In the absence of Slimb, each mother centrosome can give rise to several daughters in one go, leading to an excess of centrosomes in the cell.

In recent years, Monica's group has produced several important findings relating to centrosome control: they identified another molecule, SAK, as the trigger for the formation of centrosomes. When SAK is absent, there are no centrosomes, whereas if SAK is overproduced, the cell has too many centrosomes. These results were published in the prestigious journals Current Biology and Science, in 2005 and 2007. Now, the group has discovered the player in the next level up: Slimb mediates the destruction of SAK, and in so doing, ultimately controls the number of centrosomes in a cell.

Monica explains, 'We carried out these studies in the fruit fly, but we know
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